Molecular Cloning, Characterization, and Expression of a Human 14-kDa Lectin

Full length cDNAs coding for a 14-kDa β-galactoside binding lectin have been isolated from HL-60 cells and human placenta. Oligonucleotide probes based on a pentapeptide present in several partial sequences of homologous human lectins were used to screen a λ GT10 HL-60 cDNA library. The HL-60 cDNA clones that were isolated were used to design a synthetic primer representing the 3′-untranslated region of the HL-60 lectin. This primer was then used to synthesize a λ GT10 human placenta cDNA library, and restriction fragments of the HL-60 cDNA clones were used to screen the library. The cDNA clones for both HL-60 and placenta lectin had identical sequences with short 5′- and 3′-untranslated regions and coded for a 135-amino acid protein which lacks a hydrophobic signal peptide sequence. Biochemical data show that, despite the presence of a possible N-linked glycosylation site, the protein is not glycosylated. Northern and Southern blot analyses indicate that the 14-kDa lectin is encoded for by a single gene. The lectin cDNA was expressed in Escherichia coli and biologically active protein was purified from cell lysates by affinity chromatography.